Disruption of the anterior thalamic head direction signal following reduction of the hippocampal theta rhythm.

There is overlap between the structures containing head direction (HD) cells and those mediating the hippocampal theta rhythm, and both signals are thought to play an important role in spatial navigation. Previous research has shown that reversible inactivation of the medial septum attenuates hippocampal theta activity and disrupts path integration-based navigation. Although the HD signal reflects navigational performance, it is unclear whether theta rhythm contributes to the direction-specific activity of HD cells.

NMDA blockade inhibits experience-dependent modification of anterior thalamic head direction cells.

Head Direction (HD) cells of the rodent Papez circuit are thought to reflect the spatial orientation of the animal. Because NMDA transmission is important for spatial behavior, we sought to determine the effects of NMDA blockade on the basic directional signal carried by HD cells and on experience-dependent modification of this system. In Experiment 1, HD cells were recorded from the anterior dorsal thalamus in female Long-Evans rats while they foraged in a familiar enclosure following administration of the NMDA antagonist CPP or saline.

Region-Specific Summation Patterns Inform the Role of Cortical Areas in Selecting Motor Plans.

Given an instruction regarding which effector to move and what location to move to, simply adding the effector and spatial signals together will not lead to movement selection. For this, a nonlinearity is required. Thresholds, for example, can be used to select a particular response and reject others.

Impairment of the anterior thalamic head direction cell network following administration of the NMDA antagonist MK-801.

Head direction (HD) cells, found in the rodent Papez circuit, are thought to form the neural circuitry responsible for directional orientation. Because NMDA transmission has been implicated in spatial tasks requiring directional orientation, we sought to determine if the NMDA antagonist dizocilpine (MK-801) would disrupt the directional signal carried by the HD network. Anterior thalamic HD cells were isolated in female Long-Evans rats and initially monitored for baseline directional activity while the animals foraged in a familiar enclosure.

Magnetic field polarity fails to influence the directional signal carried by the head direction cell network and the behavior of rats in a task requiring magnetic field orientation.

Many different species of animals including mole rats, pigeons, and sea turtles are thought to use the magnetic field of the earth for navigational guidance. While laboratory rats are commonly used for navigational research, and brain networks have been described in these animals that presumably mediate accurate spatial navigation, little has been done to determine the role of the geomagnetic field in these brain networks and in the navigational behavior of these animals. In Experiment 1, anterior thalamic head direction (HD) cells were recorded in female Long-Evans rats while they foraged in an environment subjected to an experimentally generated magnetic field of earth-strength intensity, the polarity of which could be shifted from one session to another.

Combined blockade of serotonergic and muscarinic transmission disrupts the anterior thalamic head direction signal.

Head direction (HD) cells have been speculated to be part of a network mediating navigational behavior. Previous work has shown that combined administration of serotonergic and muscarinic antagonists eliminates hippocampal theta activity and produces navigational deficits more severe than blockade of either neurotransmitter system alone. The authors sought to assess this effect on the directional characteristics of HD cells.

Where am I and how will I get there from here? A role for posterior parietal cortex in the integration of spatial information and route planning.

The ability of an organism to accurately navigate from one place to another requires integration of multiple spatial constructs, including the determination of one's position and direction in space relative to allocentric landmarks, movement velocity, and the perceived location of the goal of the movement. In this review, we propose that while limbic areas are important for the sense of spatial orientation, the posterior parietal cortex is responsible for relating this sense with the location of a navigational goal and in formulating a plan to attain it. Hence, the posterior parietal cortex is important for the computation of the correct trajectory or route to be followed while navigating.

Landmark control and updating of self-movement cues are largely maintained in head direction cells after lesions of the posterior parietal cortex.

Head direction (HD) cells discharge as a function of the rat's directional orientation with respect to its environment. Because animals with posterior parietal cortex (PPC) lesions exhibit spatial and navigational deficits, and the PPC is indirectly connected to areas containing HD cells, we determined the effects of bilateral PPC lesions on HD cells recorded in the anterodorsal thalamus. HD cells from lesioned animals had similar firing properties compared to controls and their preferred firing directions shifted a corresponding amount following rotation of the major visual landmark.

Preparatory delay activity in the monkey parietal reach region predicts reach reaction times.

To acquire something that we see, visual spatial information must ultimately result in the activation of the appropriate set of muscles. This sensory to motor transformation requires an interaction between information coding target location and information coding which effector will be moved. Activity in the monkey parietal reach region (PRR) reflects both spatial information and the effector (arm or eye) that will be used in an upcoming reach or saccade task.

Degradation of head direction cell activity during inverted locomotion.

Head direction (HD) cells in the rat limbic system carry information about the direction the head is pointing in the horizontal plane. Most previous studies of HD functioning have used animals locomoting in an upright position or ascending/descending a vertical wall. In the present study, we recorded HD cell activity from the anterodorsal thalamic nucleus while the animal was locomoting in an upside-down orientation.

Rat head direction cell responses in zero-gravity parabolic flight.

Astronauts working in zero-gravity (0-G) often experience visual reorientation illusions (VRIs). For example, when floating upside down, they commonly misperceive the spacecraft floor as a ceiling and have a reversed sense of direction. Previous studies have identified a population of neurons in the rat's brain that discharge as a function of the rat's head direction (HD) in a gravitationally horizontal plane and is dependent on an intact vestibular system.

Hippocampal place cell instability after lesions of the head direction cell network.

The occurrence of cells that encode spatial location (place cells) or head direction (HD cells) in the rat limbic system suggests that these cell types are important for spatial navigation. We sought to determine whether place fields of hippocampal CA1 place cells would be altered in animals receiving lesions of brain areas containing HD cells. Rats received bilateral lesions of anterodorsal thalamic nuclei (ADN), postsubiculum (PoS), or sham lesions, before place cell recording.

Non-spatial, motor-specific activation in posterior parietal cortex.

A localized cluster of neurons in macaque posterior parietal cortex, termed the parietal reach region (PRR), is activated when a reach is planned to a visible or remembered target. To explore the role of PRR in sensorimotor transformations, we tested whether cells would be activated when a reach is planned to an as-yet unspecified goal. Over one-third of PRR cells increased their firing after an instruction to prepare a reach, but not after an instruction to prepare a saccade, when the target of the movement remained unknown.

Eye-hand coordination: saccades are faster when accompanied by a coordinated arm movement.

When primates reach for an object, they very often direct an eye movement toward the object as well. This pattern of directing both eye and limb movements to the same object appears to be fundamental to eye-hand coordination. We investigated interactions between saccades and reaching movements in a rhesus monkey model system.